System and Method for Integrally Casting Multilayer Metallic Structures

ABSTRACT

A process of making a multilayer metallic casting includes steps of simultaneously forming a first layer of a first metallic material and a second layer of a second metallic material using a high speed continuous casting process, and continuously bonding the first and second layers to form a integrally cast multilayer metallic casting. The process may be performed using a twin-roll type continuous casting system having a continuous casting mold that includes a first mold compartment for receiving a molten first metallic material and a second mold compartment for receiving a molten second metallic. The molten first and second types of metallic material are quickly solidified into semi-solid shells and are pressed together by opposed casting rolls, creating a metallurgical bond between the first and second types of metallic material in order to form an integrally cast multilayer metallic casting. The process permits the high speed efficient manufacturing of near net shape multilayer metallic castings.

This application is a continuation-in-part of U.S. patent application Ser. No. 12/539,333, filed Aug. 11, 2009, the entire disclosure of which is hereby incorporated by reference as if set forth fully herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates broadly to the field of high speed metals casting and fabrication, and more specifically to systems and methods for integrally casting a structure, and in particular a near net shape structure, that has more than one layer.

2. Description of the Related Technology

Dual layer metal sheets are commonly used in applications where the required properties for one side of the metal sheet are different than those properties required for the opposite side. Consideration is given to the chemical, physical, or economic requirement of the product being manufactured, whether it is for the purpose of strength, corrosion resistance, or any one of many other variables. As such those two metals are produced separately and then bonded to each other through various methods such as roll bonding or explosion welding in order to get a strong metallurgical bond.

An example of one such application can be found in U.S. Pat. No. 6,360,936 B1 issued on Mar. 26, 2002 for a composite sheet of maraging steel that is resistant to penetration by flying debris caused by explosives. In order to achieve the type of bond necessary for this critical application steps are taken to remove metal from the two surfaces being bonded by machining and explosive bonding the two materials together followed by subsequent rolling. Alternative steps that may be used to bond the two materials together for this application include peripherally welding the first and second plates together and producing a vacuum between them before roll-bonding the two materials together and into the final shape.

Explosive bonding of two or more materials is earlier described in U.S. Pat. No. 3,137,937 issued on Jun. 23, 1964 whereby the metal layers are separated from each other and then explosively propelled together at an impact velocity adequate to permanently bond the materials together. High powered electron scanning microscopes have since confirmed mass conversion calculations that likely indicate an extremely fine line of melting of the two materials occurs at the bond line.

A record of roll bonding can be found in U.S. Pat. No. 2,522,408 issued on Sep. 12, 1950, which describes a method of cold welding various materials together through the application of extremely high pressure at or above the flow point of the metals. Another example of roll bonding using heat and pressure is described in U.S. Pat. No. 2,414,511 issued on Jan. 21, 1947.

When considering the numerous manufacturing steps taken to individually produce each metal and the further steps taken to bond and process those metals into the final net shape, it is easy to understand the high cost of dual layer metal sheets. Large amounts of energy are consumed in the metals industry during melting and preparing liquid metals for casting and again for rolling and shaping those cast metals into the flat sheet product. Dual layer metal sheets use 2 to 3 times the manufacturing energy as single-layer metal sheets.

Typically dual layer metals are made of thick or thin slabs produced individually at cast speeds ranging from 0.5 to 8.0 meters per minute. Much higher casting speeds ranging from 40 to 160 meters per minute are typically achieved by twin-roll strip casting.

The following chart illustrates typical casting speeds for strip, thin slab, and thick slab casting.

Strip Thin slab Thick slab Strip thickness, mm 1.6 50 220 Casting speed, m/min 80 6 2

Each of the three different casting methods can be used to produce a coil of steel for example with a final net shape of 1.2 mm thickness. However the amount of rolling energy required to reduce the thick slab from 220 mm thickness down to 1.2 mm thickness is much greater than the rolling energy required to reduce a near net shape of 1.6 mm thickness down to 1.2 mm thickness. Dual-layer metals produced from thin or thick slabs are not cost effective due to the high levels of energy required for rolling.

There is clearly a need for a low-cost method of producing a dual layer metal sheet with a strong metallurgical bond.

A need exists for a system and method that will permit high speed fabrication of near net shape multilayer metallic structures such as sheets or thin plates more cost-effectively than has heretofore been achieved.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a system and method that will permit high speed fabrication of multilayer metallic structures such as sheets or thin plates more cost-effectively than has heretofore been achieved.

It is further an object of one aspect of the invention to provide a method of simultaneously continuous casting two different metal materials, which can be different alloys, on opposing sides of a dual-cavity mold into a near-net shape and continuously bonding one side of each of those two metals together into a dual layer metal sheet with a strong metallurgical bond of cohesion.

It is also an object of one aspect of this invention to simultaneous continuous cast two different metal alloys and continuously bond them together while one side of each is still in a molten or semi-molten state whereby the final solidification occurs with some mixing of the two materials thus forming a permanently fused dual layer sheet.

In order to achieve the above and other objects of the invention, a method of making a multilayer metallic casting according to a first aspect of the invention includes steps of simultaneously forming a first layer of a first metallic material and a second layer of a second metallic material using a high speed continuous casting process; and continuously bonding the first and second layers to form a integrally cast multilayer metallic casting.

A method of making a multilayer metallic casting according to a second aspect of the invention includes steps of simultaneously forming a first layer of a first metallic material and a second layer of a second metallic material; and continuously bonding the first and second layers to form a final integral multilayer metallic casting that is in near net shape form.

These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatical depiction of a system for making a multilayer metallic cast structure that is constructed according to a first embodiment of the invention;

FIG. 2 is a diagrammatical depiction of a mold assembly that is preferably used in the embodiment that is shown in FIG. 1;

FIG. 3 is a diagrammatical depiction of a broader system for making a multilayer metallic cast structure that may incorporate the mold assembly that is depicted in FIG. 2; and

FIG. 4 is a diagrammatical depiction of a system and method for making a multilayer metallic cast structure using a belt casting configuration that is constructed according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to FIG. 1, a system 10 for making a multilayer metallic integrally cast structure includes a continuous casting mold 12, a first tundish 14 for supplying a molten first type of metallic material to the continuous casting mold 12 and a second tundish 16 for supplying a molten second type of metallic material to the continuous casting mold 12.

As will be described in greater detail below, and particularly in reference to FIG. 2, system 10 is constructed and arranged to continuously form by casting an integral multilayer metallic casting 48 by simultaneously forming a first layer 50 of a first type of metallic material and a second layer 52 of a second type of metallic material that are metallurgically bonded together using a continuous casting process. The integral multilayer metallic casting 48 is preferably a dual-layer structure, although it is anticipated that casting of more than two layers could potentially be achieved according to the principles of the invention as is described herein.

As is shown in FIG. 1, system 10 includes a vertical guide roll rack 18 for receiving the cast multilayer metallic structure 48, which is preferably shaped in near net shape form as a strip, sheet or a thin plate, from the continuous casting mold 12 and guiding it vertically downward. Near net shape means that the initial production of the item is very close to the final (net) shape, reducing the need for further processing such as rolling, which significantly saves time and energy usage.

The direct casting of the structure 48 in near net shape form is preferably performed at a high casting speed that is substantially within a range of about 40 to about 160 meters per minute, more preferably substantially within a range of about 60 to about 120 meters per minute and most preferably substantially within a range of about 80 to about 100 meters per minute. This provides significant benefits in terms of reduced energy costs and reduction of necessary downstream processing.

In the preferred embodiment, the multilayer cast structure 48 is a thin sheet having two integral layers. System 10 further includes a bending roll unit 20, a curved roll rack 22 and a straightener roll rack 24 for gradually re-orienting the multilayer casting 48 from the cast vertical orientation into a horizontal orientation.

A horizontal roll rack 26 guides the continuous sheet of multilayer metallic casting unit 48 into a cutting, rolling and coiling assembly 28, where it is maybe subdivided into smaller portions for integration into a finished product or for further processing. The curvature of the system 10 is preferably over a large radius (at least 10 meters) before it reaches a horizontal position. A series of driven roll pairs may be periodically spaced along transport path to support the weight and control the withdrawal speed of the multilayer casting from the continuous casting mold 12.

Referring now to FIG. 2, it will be seen that the continuous casting mold 12 preferably includes a first mold compartment 30 and a second mold compartment 32 that is separated from the first mold compartment 30 by a separating dam 38. The separating dam is preferably fabricated from a material such as a refractory or a coated refractory material. To cast wider products, the refractory separating dam 38 may have a refractory metal core for additional strength, made of tungsten, molybdenum, niobium, tantalum, rhenium or one of the other Group 4, 5, 6 or 7 elements. The continuous casting mold 12 is accordingly partitioned lengthwise by the separating dam 38, with the length substantially corresponding to the desired near net shape width of the product 48 that is to be cast.

The first mold compartment 30 is constructed and arranged to hold a first molten metallic material 34 received from the first tundish 14, and is defined in part by a first casting roll 44. The second mold compartment 32 is constructed and arranged to hold a second molten metallic material 36 received from the second tundish 16, and is defined in part by a second casting roll 46. A casting throat 37 is defined at a lower portion of the continuous casting mold 12 as the gap between the two casting rolls 44, 46.

The first casting roll 44 is preferably liquid-cooled and is mounted to rotate in a clockwise direction as viewed in FIG. 2. The second casting roll is also preferably liquid-cooled and is mounted to rotate in a counterclockwise direction as viewed in FIG. 2.

The first molten metallic material 34 preferably is formulated from an alloy of steel, aluminum, magnesium, copper, or another metallic material capable of being manufactured by the twin-roll casting process. The second molten metallic material 36 preferably is formulated from another alloy of that same base metal group with a substantially similar coefficient of thermal expansion or shrinkage rate as is commonly used in continuous casting. Alternatively, two molten metallic materials with substantially similar coefficients of thermal expansion but from entirely different base metal groups may be bonded together using this process, i.e. a copper-based alloy on one side and a stainless steel alloy on the other.

The lowermost end of the separating dam 38 terminates at a preferably tapered tip 40 that is proximate the casting throat 37, and in the preferred embodiment is provided with a heating element 42, which is preferably an electric resistance type heating element.

In operation, a multilayer metallic integral casting structure 48 having a metallurgically bonded interface 58 is continuously fabricated as a high speed thin strip having an a first layer 50 that is fabricated from the first metallic material and second layer 52 that is fabricated from the second metallic material using the continuous casting mold 12.

The molten first type of metallic material 34 in the first mold compartment 30 is quickly cooled by contact with the first casting roll 44, forming a semi-solidified shell 54 that increases in thickness as it nears the casting throat 37. Simultaneously, the molten second type of metallic material 36 in the second mold compartment 32 is quickly cooled by contact with the second casting roll 46, forming a semi-solidified shell 56 that increases in thickness as it nears the casting throat 37.

The interior surfaces of the respective shells 54, 56 are preferably heated by the heater 42 near the tapered lower tip 40 of the separating dam 38. The semi-solidified shells 54, 56 are then pressed together by the casting rolls 44, 46 at the casting throat 37, thereby forming a continuous metallurgical bond between the inner surfaces thereof and forming the integral multilayer metallic casting 48 having a metallurgically bonded interface 58 between the two layers 50, 52.

The continuous bonding of the first and second layers 50, 52 to form the metallurgically bonded interface 58 is thus performed while the first and second layers 50, 52 are still at elevated temperatures from the continuous casting process.

By heating the respective inner surfaces of the layers 50, 52 using the heater 42, the continuous bonding of the first and second layers 50, 52 to form the metallurgically bonded interface 58 may be performed while at least a portion of at least one of the first and second layers 50, 52 is in at least a semi-molten state, which facilitates the formation of the metallurgical bond between the layers 50, 52. By controlling the degree of heating that is provided by the heater 42, the amount of mixing of the first type of metallic material and the second type of metallic material that occurs during the formation of the multilayer casting at the interface 58 can be controlled.

By adjusting the cooling that is provided by the respective casting rolls 44, 46, the thicknesses of each of the first and second layers 50, 52 can also be adjusted. For example, by circulating a greater volume of coolant through the casting roll 46 than is provided to casting roll 44, the thickness of the semi-solidified shell 56 can be formed to be thicker than the shell 54, causing the second layer 52 to be formed to be thicker than the first layer 50.

Alternatively, the process described above could be performed without the heater 42, or by configuring the heater 42 so that it applies heat to only one of the inner surfaces of the respective semi-solidified shells 54, 56. Use of the heater 42 is preferred, however, because it promotes the control of the formation of a secure metallurgical bond between the layers 50, 52.

A broader system 60 for making a multilayer metallic cast structure that is constructed according to the first embodiment of the invention described above is shown in FIG. 3. System 60 includes first and second ladles 62, 64 that are adapted to respectively feed a first molten metallic material and a second molten material into first and second tundishes 66, 68. The first and second tundishes 66, 68 are adapted to continuously feed the respective molten first and second metallic materials respectively through distribution nozzles 70, 72 into the first and second mold compartments 30, 32 of the continuous casting mold 12, which is otherwise constructed identically to the continuous casting mold 12 described above.

According to an alternative embodiment of the invention that is shown in FIG. 4, a twin-belt casting system 90 could be used to continuously fabricate the integral multilayer metallic casting 48 in lieu of the roll casting system 10. The twin-belt casting system 90 preferably includes a first belt casting assembly 92 for casting a first metallic shell 94 and a second belt casting assembly 96 for casting a second metallic shell 98. The first belt casting assembly 92 includes a first upper casting belt 100 that travels about rollers 102, 104, and a first lower casting belt 106 that travels about rollers 108, 110. The second belt casting assembly includes a second upper casting belt 112 that travels about rollers 114, 116 and a second lower casting belt 118 that travels about rollers 120, 122.

The lower casting belts 106, 118 are constrained by rollers 110, 120 to form a casting throat in which the inner surfaces of the shells 94, 98 are pressed together in order to facilitate metallurgical bonding of the shells 94, 98.

In twin-belt casting, the initial solidification of the shells 94, 98 occurs once on the respective lower belt 106, 118 and once on the respective 100, 112 upper belt, and those two shells 94, 98 continue to grow from the liquid center of the shell until they meet at the center. Thickness of either wall of either shell 94, 98 can be adjusted by adjusting the temperature of the respective belt. In addition, by keeping the upper belts 100, 112 relatively hot, the side of the respective shells that is to be bonded with the other shell in order to form the multilayer metallic casting 48 could be kept soft in a semi-molten state order to facilitate metallurgical bonding.

A heating and guiding unit 124 is also preferably provided that includes a source of heat such as an electric resistance heater for applying additional heat to the upper surface of one or both of the shells 94, 98. Further softening or re-melting of the upper shell surfaces by the heating and guiding unit 124 could further facilitate metallurgical bonding. By keeping the upper shell on each side from growing very fast by keeping the belt 100, 112 hot and/or by using the heating or guiding unit 124, it would also be possible to use the system 90 to continuously cast in a horizontal or near-horizontal configuration.

It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A method of making a multilayer metallic casting, comprising: simultaneously forming a first layer of a first metallic material and a second layer of a second metallic material using a high speed continuous casting process; and continuously bonding said first and second layers to form a integrally cast multilayer metallic casting.
 2. A method of making a multilayer metallic casting according to claim 1, wherein said step of continuously bonding said first and second layers is performed while said first and second layers are still at elevated temperatures.
 3. A method of making a multilayer metallic casting according to claim 2, wherein said step of continuously bonding said first and second layers is performed while at least a portion of one of said first and second layers is in at least a semi-molten state.
 4. A method of making a multilayer metallic casting according to claim 3, further comprising a step of providing additional heating to at least one surface of at least one of said first and second layers that is to be bonded to a surface of the other of said first and second layers in order to form the integrally cast multilayer metallic casting.
 5. A method of making a multilayer metallic casting according to claim 1, wherein said step of simultaneously forming a first layer of first layer of metallic material and a second layer of a second type of metallic material using a continuous casting process is performed using a continuous casting mold having a first mold compartment holding molten metallic material of the first type; a second mold compartment holding molten metallic material of the second type; and a separating dam defining a divider between said first and second mold compartments.
 6. A method of making a multilayer metallic casting according to claim 1, wherein said step of simultaneously forming a first layer of the first type of metallic material and a second layer of the second type of metallic material is performed using a continuous casting machine having a first casting roll for forming and cooling one of said first and second layers.
 7. A method of making a multilayer metallic casting according to claim 6, wherein said step of simultaneously forming a first layer of the first type of metallic material and a second layer of the second type of metallic material is further performed using a second casting roll for forming and cooling the other of said first and second layers.
 8. A method of making a multilayer metallic casting according to claim 1, said first type of metallic material and said second type of metallic material are not the same material.
 9. A method of making a multilayer metallic casting according to claim 1, wherein said high speed continuous casting process operates at a casting speed that is substantially within a range of about 40 to about 160 meters per minute.
 10. A method of making a multilayer metallic casting according to claim 9, wherein said high speed continuous casting process operates at a casting speed that is substantially within a range of about 60 to about 120 meters per minute.
 11. A method of making a multilayer metallic casting according to claim 10, wherein said high speed continuous casting process operates at a casting speed that is substantially within a range of about 80 to about 100 meters per minute.
 12. A method of making a multilayer metallic casting according to claim 1, wherein said continuous casting process is performed to produce a casting that is in near net shape form.
 13. A method of making a multilayer metallic casting, comprising: simultaneously forming a first layer of a first metallic material and a second layer of a second metallic material; and continuously bonding said first and second layers to form a final integral multilayer metallic casting that is in near net shape form.
 14. A method of making a multilayer metallic casting according to claim 13, wherein said step of continuously bonding said first and second layers is performed while said first and second layers are still at elevated temperatures.
 15. A method of making a multilayer metallic casting according to claim 14, wherein said step of continuously bonding said first and second layers is performed while at least a portion of one of said first and second layers is in at least a semi-molten state.
 16. A method of making a multilayer metallic casting according to claim 15, further comprising a step of providing additional heating to at least one surface of at least one of said first and second layers that is to be bonded to a surface of the other of said first and second layers in order to form the integrally cast multilayer metallic casting.
 17. A method of making a multilayer metallic casting according to claim 13, wherein said step of simultaneously forming a first layer of first layer of metallic material and a second layer of a second type of metallic material using a continuous casting process is performed using a continuous casting mold having a first mold compartment holding molten metallic material of the first type; a second mold compartment holding molten metallic material of the second type; and a separating dam defining a divider between said first and second mold compartments.
 18. A method of making a multilayer metallic casting according to claim 13, wherein said step of simultaneously forming a first layer of the first type of metallic material and a second layer of the second type of metallic material is performed using a continuous casting machine having a first casting roll for forming and cooling one of said first and second layers.
 19. A method of making a multilayer metallic casting according to claim 18, wherein said step of simultaneously forming a first layer of the first type of metallic material and a second layer of the second type of metallic material is further performed using a second casting roll for forming and cooling the other of said first and second layers.
 20. A method of making a multilayer metallic casting according to claim 13, said first type of metallic material and said second type of metallic material are not the same material. 